The present invention relates to a coating layer forming apparatus for forming a coating layer on a surface to be coated of a part and a method to form the coating layer.
More particularly, it relates to a coating layer forming apparatus for obtaining a coating layer improved in dimensional accuracy of a sliding surface and a lubricating effect of a sliding surface of a piston etc. and a method to form a coated layer.
Japanese Unexamined Patent Publication (Kokai) No. 8-173893 discloses a coating layer forming apparatus and a method to form a coated layer. An explanation will be given of the coating device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-173893 with reference to FIG. 1.
A coating device 100 shown in FIG. 1 is provided with a coating container 101 above a base material 104. The coating container 101 is filled with a coating solution 102. Below the coating container 101 at the two ends of the base material 104 is arranged a shaft bearing support plate 103 for rotatably supporting the base material 104. The shaft bearing support plate 103 was mounted on it a not shown drive motor. The drive motor makes the base material 104 rotate in the illustrated clockwise arrow direction R.
Since the coating solution 102 flows out from a nozzle of the coating container 101, the coating surface 105 of the base material 104 made to rotate by the not illustrated drive motor is coated on its entire surface as if being wrapped by it along with the rotation. To level the thickness of coating solution 102 coated on the surface to be coated 105, a blade 106 set to an inclined angle xcex8 of 135xc2x0 with respect to a tangential direction of rotation of the base material 104 is provided at the surface to be coated 105.
A front end 106a of the blade 106 is held at a clearance of 100 xcexcm from the coating surface 105. Further, the front end 106a of the blade 106 is formed into a stepped portion so as to become thinner. The blade 106 is fixed to a block 107. The excess amount of the coating solution 102 coated on the base material 104 is collected by the blade 106 and made to flow downward via an inclined surface of the blade 106 while the not shown drive motor makes the base material 104 rotate five to six times at 200 rpm. A solution receiving mechanism 108 for accommodating excess amount of the coating solution flowing down from a rear end of the blade 106 is provided.
The coating device 100 is simply structured and operates by a simple principle, but suffers from the following disadvantages.
Since the coating solution 102 accommodated in the coating container 101 is made to drop from the nozzle of the coating container 101 on to the coating surface 105 of the rotating base material 104 by the free-fall dropping method, the amount dropped changes in accordance with the amount and viscosity of the coating solution 102 accommodated. Therefore, to prevent insufficient coating, a large amount of the coating solution 102 is made to drip on to the coating surface 105 of the substrate 104 and the excess amount of the coating solution is removed by the blade 106 and stored in the solution receiving mechanism 108, but the amount of the coating solution 102 consumed becomes largexe2x80x94which is uneconomical.
If a large amount of coating solution 102 is deposited on the coating surface 105 of the substrate 104, it cannot be fully removed by the blade 106, a coating of a uniform thickness cannot be formed, and it becomes difficult to improve the quality of the coating by reducing the speed of the substrate 104. If the speed of the substrate 104 is increased, the time for forming the coating becomes longer and the productivity is lowered.
The blade 106 is attached inclined so as to guide the excess coating solution 102 to the solution receiving mechanism 108 along its surface, the blade 106 is inclined to a blunt angle xcex8=135xc2x0 with the rotating coating surface 105 of the substrate 104. That is, the blade 106 only scrapes off the excess coating solution 10 of the surface of the coating surface 105 of the substrate 104. The coating solution 102, however, has viscosity, so the amount of the coating solution removed by the blade 106 changes in accordance with its viscosity. The thickness of the remaining coating solution on the coating surface 105 also changes in accordance with the viscosity. In this way, the quality of the coating film has a large dependence on the viscosity.
As apparatuses other than the above coating layer forming apparatus, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-26081 and Japanese Unexamined Patent Publication (Kokai) No. 5-147189 disclose a screen printing method to coat material on a piston or other members. In a screen printing apparatus, however, the thickness of coated layer of the coating material becomes thin. To form a coating layer obtaining a sufficient sliding function, repeated coating is necessary. Therefore, there are problems that multiple coating is required, the number of steps in the process is increased, an increase in the coating facilities becomes necessary, and that the process of production becomes expensive.
An object of the present invention is to provide a coating layer forming apparatus able to minimize the amount of the coating solution coated and to improve the accuracy of thickness of the coating layer formed by the coating solution and a method of formation thereof.
Another object of the present invention is to provide a coating layer forming apparatus able to improve the quality and the dimensional accuracy of the coated layer by a coating blade even if the coating accuracy for coating the coating solution on the coating surface of a part is insufficient and a method of formation thereof.
Still another object of the present invention is to provide a coating layer forming apparatus able to improve the accuracy of thickness and quality of the coated layer regardless of the viscosity of the coating solution and a method of formation thereof.
Still another object of the present invention is to provide a coating layer forming apparatus able to improve the production efficiency of the formation of the coating layer and minimize the amount of the coating solution used and a method of formation thereof. Further, an object of the present invention is to provide a coating layer forming apparatus able to simplify the configuration of the coating layer forming apparatus and a method of formation thereof.
The coating layer forming apparatus according to the first aspect of the present invention comprises; a support portion for supporting in attachable, detachable and alignmentable manner, two ends of a part on which a coating layer is to be formed; a rotatingly support device having a rotation drive portion for making said part supported by the support portion rotate; a feeder for feeding a coating solution to a surface to be coated of the part supported by the support portion; a layer forming device having a coating former inclined at an angle (xcex8) of 30xc2x0 to 70xc2x0 with respect to a tangential direction of rotation of said coating solution fed from the feeder to the coating surface and having a front end held at a clearance of a coating solution thickness from the coating surface; and a coating removing means for removing the amount of the coating solution deposited on the coating former of the layer forming device from the coating former.
The coating layer forming apparatus of the present invention explained above coats the coating solution coated on the coating surface by the layer forming device, while making the outer diameter of the coating layer uniform. At this time, even if the coating solution is coated nonuniformly on the coating surface, since the coating solution accumulated as the excess coating solution at the triangularly shaped space between the coating former and the coating surface of the part flows to the coating surface where it is insufficient, the coating layer is uniformly coated. Further, since the coating solution can be pressed to the coating surface by the coating former, the dimensional accuracy for the outer diameter of the coating layer is improved. Further, even if the coating solution of the coating surface coated from the feeder is not uniform, since the coating former levels the excess coating solution to make it uniform, it is possible to coat the coating solution in a ring shape via a feed nozzle and possible to form a high precision coating layer even if coating via an immersion tank filled with the coating solution is performed.
In the coating layer forming apparatus of the present invention, the coating removing means removes excess coating solution deposited on the coating former after the coating former of the layer forming apparatus forms the coating solution to the thickness of the coating layer.
As shown in this configuration, when the coating solution is deposited on the coating former, since the coating solution deposited on the coating former is removed by the coating removing means, the dimensional accuracy of the coating layer is improved and it is possible to prevent formation of projections on the surface of the coating layer. Further, it is possible to secure excess coating solution at the coating former during formation and press the coating solution, the dimensional accuracy and quality of the coating layer can be improved.
Further, in the coating layer forming apparatus of the present invention, the coating removing means is comprised of an outlet at the layer forming side of the coating former provided at the layer forming device.
In shown in this configuration, by directly forming the coating removing means at the coating former, the excess coating solution is flowed through the outlet, and thus it is possible to secure a substantially constant amount of the excess coating solution and coat it on the coating surface. Also, the excess coating solution is reduced in stages. Therefore, it is possible to finish the surface of the coating layer with a high accuracy.
Further, in the coated layer forming apparatus of the present invention, the layer forming device has a first coating former and an approximately parallel second coating former and has an outlet at the second coating former.
As shown in this configuration, by providing the second coating former provided with the outlet in addition to the first coating former, it is possible to form the coating solution in two stages to improve the accuracy of the coating layer. Further, when the excess coating solution becomes more than a certain amount in the first coating former, the first coating former is pulled back and solution is removed by the coating removing means. During this time, the second coating former forms the coating solution into a coating layer. By alternately removing the excess coating solution deposited onto the first and second coating formers in this way, it is possible to finish the surface of the coating layer with a high accuracy.
Further, the coating layer forming apparatus according to the second aspect of the present invention comprises; a support portion for supporting in attachable, detachable and alignmentable manner, two ends of a part on which a coating layer is to be formed; a rotatingly support device having a rotation drive portion for making said part supported by the supports rotate; a feeder portion for feeding a coating solution to a coating surface of the part supported by the rotating support device; a rotating layer forming device provided along a circumferential direction of a rotation body with a plurality of blade-shaped coating formers each inclined in an angular range of 30xc2x0 to 70xc2x0 with respect to a tangential direction of rotation of said coating solution fed from the feeder to the coating surface and formed at a clearance of the coating layer thickness from the coating surface; and a washing tank where the coating formers are washed below the rotating layer forming device, the rotation direction of the rotating layer forming device being opposite to that of the rotation of the part.
Since the coating layer forming apparatus provides the rotation body with the first, second, third, and further coating formers inclined and the coating former is configured so as to be washed in a washing tank, it is possible to finish the coating layer while either washing the coating solution deposited on the coating former or washing it at the end of each forming process. Therefore, it is possible to form a high precision coating layer.
Further, in the coating layer forming apparatus of the present invention, the rotating layer forming device successively intermittently rotates for each first forming step where the plurality of coating formers form said coating solution into the coating layer.
As seen in this configuration, when the coating former forms the coating layer and excess coating solution is deposited on the coating former, the layer forming device rotates and finishes the coating layer by the next coating former.
Further, in the coating layer forming apparatus according to the present invention, the rotation drive portion of the rotating support device makes the part rotate in a range of 5 to 200 rotations per minute in one forming step and makes the rotational speed larger before making the coating formers move away from the coating layer.
As in this configuration, when coating the coating solution on the coating surface, the part is rotated at a low rotational speed, while when forming and finishing the coating layer, it is rotated at a higher speed than the first low rotation and the coating former is pulled away from the coating layer surface so that projections are not formed on the surface of the coating layer.
The method of forming a coating layer of the present invention comprises centering and supporting two ends of a part and making a coating surface rotate by a rotating support device, coating a coating solution from a feeder on the coating surface, forming a coating layer by a coating former inclined at an inclined angle of 30xc2x0 to 70xc2x0 with respect to a tangential direction of rotation of the coating solution coated on the coating surface and held at a clearance of the coating layer thickness from the coating surface, removing the excess coating solution deposited on the coating former via a coating removing means, and forming a coating layer of a next forming step.
The method of forming a coating layer of the present invention arranges the coating former inclined in the range of 30xc2x0 to 70xc2x0 with respect to the rotating tangential direction of the coating solution to form the coating layer while interposing excess coating solution at the coating former and, when the excess coating solution is deposited more than necessary or when shifting to the next forming process, removes the coating former via the coating removing means and finishes the outer surface of the coating layer.
In the method of forming a coating layer of the present invention, the coating solution has a viscosity of 100 CP to 20,000 CP at a coating temperature of 25xc2x0 C. and a shear rate of 100 Sxe2x88x921.
By doing this, it becomes possible to form a coating layer with a good surface precision by a coating solution having a broad range of viscosity.
The coating solution has an organic resin as a binder dissolved or dispersed in water or an organic solvent and a PTFE powder as a solid lubricant, including 10 to 100 parts by weight of PTFE powder based on 100 parts by weight of the binder.
By doing this, the PTFE powder provides an excellent lubricating effect and it becomes possible to form a coated layer with a good surface precision.